Objective: To evaluate the contribution of three provider practices to underimmunization of children with financial coverage for vaccines.
Design: Retrospective cohort study of children in a large health maintenance organization, based on computerized databases and chart review.
Setting: Large health maintenance organization in northern California.
Patients: The population included 24,268 children who had at least one immunization recorded in the health plan tracking system and had continuous health plan membership between 15 and 24 months of age in 1992 through 1993. The study group (N = 4691) were those who had missed one or more of the immunizations due during their second year.
Results: Most (57%) of the underimmunized children had made at least one clinic visit between 15 and 24 months of age. Among those underimmunized children who made well care visits, 90% had been partially immunized at the visit but had not been simultaneously given all vaccines for which they were eligible. When a provider did not give all possible vaccines simultaneously, there was a 9% chance that the child would go on to miss the remaining immunization. Simultaneous administration alone would have achieved full second year coverage of 30% of the underimmunized children in this population. Most underimmunized children (53%), including 35% of those children who had not made any well care visits, had made urgent visits between 15 and 24 months of age. Chart review of randomly sampled patients showed no obstacle or contraindication to immunization at 79% of urgent visits and at 71% of well care visits at which vaccines were withheld. A policy to use weekday urgent visits to promote immunization could potentially reach 27% of the underimmunized children.
Conclusions: Provider practices play an important role in underimmunization of children who have insurance coverage for vaccines. Of the three guidelines evaluated, simultaneous administration of all possible vaccines has the greatest potential effectiveness to improve coverage rates in this population. Other guidelines, such as immunizing at urgent visits, are potentially effective but their costs and logistics need further study.